Sciencemadness Discussion Board

Are Magnesium Metal Flakes Spontaneously Reactive with Any Oxidizers?

holmes1880 - 22-1-2011 at 21:29

Are their any known spontaneous reactions between Mg flakes from firestarters(so, coarse grade) and nitrates(KNO3, NH4NO3) or energetics such as MHN, ETN, TNP?

I have a tiny sample of ETN and Mg mixed sitting in a corner. Impact sensitivity seems same/slightly elevated, but that's expected since Mg itself sparks upon impact. Friction sensitivity hasn't changed. I also mixed KNO3 with Mg with no effect.

Mg burns as hot as any thermite-3000C and has ignition temperature of around 600C. The latter is probably lower depending on the powder grain.

[Edited on 23-1-2011 by holmes1880]

mabuse_ - 23-1-2011 at 03:48

NH4NO3 and Mg is a bad combination.
Wet Mg can ignite. A least it's going to degrade very fast.

KNO3 should be fine, but the Mg will degrade over time.

Bert - 23-1-2011 at 06:39

There is a long and well known history of accidental fires due to contact between pyrotechnic oxidizers and Mg powders in manufacturing. SOP is to coat such powders with something before mixing.

In pyrotechnic use, pure Mg powders are coated to slow oxidation from atmospheric Oxygen as well as reduce reactions with other components of the mixtures containing them. For nitrates and Potassium perchlorate comps, tumbling the powder with linseed oil and air curing in shallow layers was common. Polyester resins are a more modern alternative. For contact with ammonium perchlorate the Mg powder is given a dichromate coating by mixing with a hot Potassium dichromate solution. Even with such coatings, water based binding should not be used for Mg compositions.

Try leaving a sample of Mg powder out for a while. It turns to oxide quite quickly- 50:50 Al:Mg alloy is a better choice for most uses, it's also quite brittle and easy to mill to small mesh size. Even the alloy will need to be dichromated for use with ammonium perchlorate though.

Aluminum is often preserved in water bound systems by the addition of small amounts of a weak acid such as boric acid to the water (basic conditions can strip the oxide coating and promote fires during mixing, drying or storage). ACIDIC CONDITIONS LEAD TO THE SAME PROBLEMS WITH MG OR Mg/Al ALLOYS. Picric acid and Mg would be a bad idea... Residual acid or acidic break down products in other explosives would not be good either.

[Edited on 23-1-2011 by Bert]

unionised - 23-1-2011 at 13:11
and a zillion similar vids

holmes1880 - 23-1-2011 at 16:34

Well, silver nitrate and Mg + H2O seems like a unique reaction. I'm getting nothing similar with KNO3 or NH4NO3. And AN reacts with Mg mostly when it's heated to a molten state.

Bert - 23-1-2011 at 18:53

1: You describe your powder as coarse, hand made flakes. Commercial pyro grade metal powders will have a LOT more surface area and therefore react faster.

2: You are working with very small quantities (and that is a GOOD thing!). Larger quantities with less surface:volume in a production setting will not be able to dissipate heat as easily- Scale matters. If you care to increase your experiment size, do it outdoors and away from other flamable materials. What you can get away with in gram size batches may turn around and bite in kilogram quantities.

3: For some REAL fun, try adding a water soluble Copper compound and lightly damping the mixture... Do it outdoors.